Patent EP 470 606 discloses tubes having an antistatic polyamide layer. This antistatic layer consists of a polyamide filled with 20% by weight of carbon black. An antistatic layer is indeed obtained, however the incorporation of 20% carbon black increases the flexural modulus of the polyamide and the tube can no longer pass the impact tests.
The advantage of carbon nanotubes is that it is sufficient to incorporate 2 to 6% by weight of them into the polyamide in order to make it antistatic and at this content the polyamide retains its mechanical properties. In particular, a tube comprising this layer is not weakened and it passes the impact tests. Patent U.S. Pat. No. 6,090,459 discloses tubes comprising layers of nylon-12 (PA-12) and/or PVDF and also comprising an antistatic PA-12 or PVDF layer. These antistatic layers are obtained by incorporating crystalline graphite fibres having a diameter of around 10 nanometers into the PA-12 or PVDF. The proportion of these fibres in the PA-12 or PVDF is between 3 and 5% by weight.
This solution provides a technical advantage over the above prior art EP 470 606, however the cost of these fibres is high. It has now been found that, in polyamide/polyolefin blends containing carbon nanotubes, the latter concentrate in the polyamide. Thus, a polyamide/polyolefin blend containing carbon nanotubes having a polyamide matrix has the same antistatic properties as a polyamide blend containing carbon nanotubes; but by containing much fewer carbon nanotubes, it is therefore less expensive. In addition, these polyamide/polyolefin blends containing carbon nanotubes form a much greater barrier to alcohol-containing fuels than polyamide/polyolefin blends not containing carbon nanotubes.